The overall goal of the present application is to develop more specific and sensitive immunoassays for circulating breast epithelial antigens (CBE-Ags), using recent information we have obtained on the antigenicity and catabolism of CBE-Ags and employing newer immunoassay systems that we have created. These novel, sensitive, and specific assays that we develop, rely first on out findings regarding the fragmentation of CBE-Ags with simultaneous clearance from the blood compartment. These fragments are much longer-lived in blood, and hence more useful, than the intact CBE-Ags. Our present incorporation of recombinant epitopes into assays for these long-lived fragments represents a totally novel approach to serum marker measurement in breast cancer. These approaches, if successful, will identify not only minimal tumor load in breast cancer, but also the 10% of the female population that will eventually develop breast cancer, in which early diagnosis could lead to life-saving, curative treatment. The creation of such assays for CBE-Ags and their fragments will depend on immunological and recombinant DNA approaches. We will screen breast cDNA libraries for sequences encoding epitopes on CBE-Ags, and especially on their catabolic fragments, both with MoAbs we already possess and with new ones generated specifically for this purpose. The corresponding cDNA will be characterized, sequenced, inserted into expression vectors, and recombinant molecules containing epitopes for the CBE-Ags and their catabolic fragments synthesized or expressed and new customized MoAbs generated for the immunoassays. These assays will then be tested in clinical trials for their sensitivity, specificity and predictive value. Since we have demonstrated both epitopic and antigenic heterogeneity and the individuality of tumor cell populations, several CBE-Ag tests will be assembled in panels to allow the choice of the most prevalent CBE-Ags for each breast tumor to be tested. The recombinant epitope assay configuration that we propose, will make the use of a panel of CBE-Ags assays both expedient and simple. Thus, we propose to develop a second generation of breast cancer serum markers to provide the desired test for the detection of residual disease in the axillary node negative patient, for early prediction of relapse in the disease-free period, for monitoring therapeutic response and possibly for screening female populations at risk.